The invention concerns a fuel tank system for a motor vehicle.
Fuel tank systems in motor vehicles are being subjected to constantly increasingly strict requirements in terms of sealing integrity of the fuel tank systems, in order to at least reduce the amount of gaseous hydrocarbons which is given off to the ambient atmosphere, either while the vehicle is moving or while the vehicle is stationary. Considerable progress has been achieved in this respect in recent years, insofar as the degree of permeability of even fuel tanks of thermoplastic material has been reduced, either by suitable treatment such as fluorination or by virtue of the tank wall being made up of a suitable structure, to such a degree that the amounts of fuel which pass into the ambient atmosphere by diffusion through the tank wall are extremely small. Thus, in regard to making the requirements in terms of sealing integrity of the entire fuel tank system ever more strict, the important consideration will essentially be that of reducing the amount of fuel which escapes in a gaseous condition through leaks or points which lack sealing integrity, for example at joints, unions, connections, closed openings in the tank wall, ducting means passing through the tank wall and closure means, and at valves. Those leakage points admittedly occur only to such an extent that they are effectively technically unavoidable and in commercial terms are not significant at all so that they could be disregarded if the situation did not involve reducing hydrocarbon-originating environmental pollution to an even greater degree than has hitherto already been the case. The above-mentioned points at which sealing integrity is lacking are connections, unions and so forth which are not disposed in the interior of the tank itself, as leakage points which occur there, for example at the connection of the pipe with which the engine of the motor vehicle is supplied with fuel to the fuel pump which is within the tank, cannot have any adverse effects because the gaseous hydrocarbons in the tank, under normal operating conditions, are passed as a component of a gas mixture through a filter which is generally in the form of an activated carbon filter, and they are adsorbed by the adsorbent in the filter.
An object of the present invention is to provide a fuel tank system which can afford a noticeable reduction in the amount of hydrocarbons discharged to the ambient atmosphere per unit of time.
Another object of the present invention is to provide a fuel tank system which is designed to reduce the escape of gaseous hydrocarbons through leakage points on the tank or on the exterior of the tank.
Still another object of the present invention is to provide a motor vehicle fuel tank system having at least one tank produced in one piece from plastic material using an extrusion blow-molding procedure wish components mounted to the exterior thereof, such that significant leakage of gaseous hydrocarbons at the mounting points of such components to the ambient atmosphere can be at least significantly reduced.
In accordance with the principles of the present invention the foregoing and other objects are attained by a tank system, more particularly for a motor vehicle, comprising at least one fuel tank, at least one connection means and/or at least one connecting conduit and/or at least one opening which is provided in the tank wall and which is closed by a closure means, and/or at least one ducting means which passes through the tank wall and/or through the closure means. The system further includes at least one cover means which is gas-tightly mounted on the outside to at least one region of the tank. The cover means, with the tank wall, defines a space which is closed off or screened with respect to the ambient atmosphere. Disposed within the space are the at least one connection means and/or at least one connecting union and/or at least one opening closed by the closure means and/or at least one ducting means passing through the tank wall and/or through the closure means.
As will become particularly apparent from the description hereinafter of preferred embodiments of the invention, the tank system according to the invention is particularly suitable for use in relation to fuel tanks which are produced in one piece, generally by an extrusion blow-molding procedure.
Because the fuel tank is produced in one piece, the interior of the tank is not unlimitedly accessible so that those components of the tank system at which joints, unions, connections, ducting means and so forth are required cannot always be arranged in the interior of the tank in the same way as would be easily possible in relation to tanks which comprise a plurality of parts and which are subsequently assembled to form the finished tank, for example by means of welding, adhesive or in some other joining procedure. It will be noted however that tanks made up of a plurality of parts, comprising plastic materials or other materials, are also provided for example with connections, openings permanently closed by suitable closure means such as covers, and so forth. The design configuration and structure of such multi-part tanks is also such that the tanks suffer from the above-discussed minor leakage points, so that using the teaching in accordance with the invention in relation also to such tanks can afford a reduction in the amount of fuel which is discharged in gaseous form to the ambient atmosphere.
It will be appreciated however that, by virtue of the simple procedure involved in manufacturing and configuring plastic tanks, such tanks appear to be particularly advantageous in terms of using the invention in relation thereto, as for example it is possible, without incurring additional expenditure, to shape the tank wall at a suitable location or possibly also at a plurality of locations in such a way as to provide a depression or a region which is delimited in some other fashion, for example by at least one projection portion extending on the outside wall surface of the tank. The depression or the region within the above-mentioned projection together with the cover means thereover defines the space which is closed off with respect to the ambient atmosphere and within which it is therefore possible to arrange those parts and regions which are critical in terms of the escape of hydrocarbons to the atmosphere and which are therefore to be screened off relative to the ambient atmosphere. It will be further appreciated that the provision of such depressions or recess configurations in the wall of the tank does not necessarily have to result in a reduction in the usable volume of the tank, as the ways in which plastic tanks can be shaped, as already referred to above, mean that the volume of the tank can possibly be increased at another location by virtue of adopting a suitable configuration for the tank wall, in order thereby to compensate for the reduction in volume initially caused by the provision of the recess or depression in the tank wall. Or the other hand however it is also to be borne in mind that the fact that the above-mentioned critical components such as unions, connections and the like can be arranged in the interior of tanks which are not made in one piece also results in a certain reduction in the usable internal volume of such a tank, unless the volume of the tank is increased at some other location in order to compensate for that volume reduction.
It will further be noted from the description hereinafter of preferred embodiments of the invention that a particular advantage which the invention achieves is that the desired result can be attained using simple means which only involve at most a minor increase in complication and expenditure. It has already been stated above that certain requirements in regard to the shaping of the tank wall do not entail any additional complication or expenditure, in particular when using an extrusion blow-molding procedure. The cover means which are required to provide the screening effect in relation to ambient atmosphere can also be produced in a simple fashion from comparatively inexpensive materials, for example an inexpensive plastic material The further requirement which is possibly to be taken into consideration, namely that the cover means must be substantially resistant to diffusion of hydrocarbons therethrough, can be attained in a simple manner, for example if the cover means, in the form of a plastic material plate or the like, is lined with an impermeable film or sheet of metal or other impermeable material, or alternatively the plastic material plate forming the cover means may be of a multi-layer or laminate configuration, wherein a layer which is at least substantially impermeable for hydrocarbons acts as a barrier layer. The cover means can also be fixed to the tank wall in a simple manner, for example by welding, if the materials forming the tank wail and the cover means are compatible, or also by adhesive or by means of some other suitable procedure.
Further objects, features and advantages of the invention will be apparent from the description hereinafter of preferred embodiments of the invention.